Four strains of Steinernema feltiae from Eastern Java, Indonesia were characterised based on morphometric, morphological and molecular data. In addition, their virulence against last instar Tenebrio molitor and heat tolerance was tested. Infective juvenile have a mean body length ranging from 749 to 792 mu m. The maximum sequence difference among the four strains was 7 bp (8.8%) in the ITS and 2 bp (0.3%) in D2D3 regions of the rDNA. All the strains are not reproductively isolated and can reproduce with European strain S. feltiae Owiplant. The lowest LC(50) was observed for strain SCM (373) and the highest for S. feltiae strain Owiplant (458) infective juveniles. All the four strains showed relatively better mean heat tolerance when compared with S. feltiae Owiplant both in adapted and non-adapted heat tolerance experiments.